mac plus half screen?

Discussion in 'Apple Collectors' started by harry2, Oct 26, 2008.

  1. harry2 macrumors newbie

    Joined:
    Oct 26, 2008
    #1
    Hi, someone may be able to help with my problem with the screen image on my mac plus? it boots fine, I get the floppy icon, and flashing ?, but the screen has disapeared, from halfway to the bottom, nothing , there is a bright line across the middle, and the image is sqeezed up tight to this line? how can I pull this line down to the bottom of the screen? or does someone know why this is happening? help!!.......... Harry.
     
  2. applefan1997 macrumors 6502

    Joined:
    Sep 2, 2005
    Location:
    Koreatown, Los Angeles, California
    #2
    There might be a adjustment screw inside the computer on the tube, but it's probably difficult to get to. Other than that, it's not a software thing.
     
  3. DZ/015 macrumors 6502a

    DZ/015

    Joined:
    Mar 23, 2003
    Location:
    New England
    #3
    This is definitely a hardware issue. You have lost vertical synch on your video signal.

    Vertical synch is carried on pin 5 of connector J4 on the logic board. Check this connector on the logic board as well as where it connects to the analog board. Sometimes just reseating this connector at both ends can clear up the issue. Oxide builds up on electrical contacts over time, preventing good conductance. Cracked solder joints are not uncommon on these old units either. If no problems are noted, take a look at Q1, Q2 and R3 on the analog board. They are part of the vertical synch circuit.

    Beware of the CRT on these old units as well. They did not contain a bleeder resistor to discharge the CRT and can hold a charge for some time.
     
  4. max¥¥ macrumors 6502a

    Joined:
    Aug 7, 2008
    Location:
    In OSX Snow Leopard / Godalming UK
    #4
    I once found a repair guide for the mac plus and se that described how to fix this problem and many outer problems i will see if i can find it

    Edit:found the guide but it didn't have the problem you described
     
  5. TheReef macrumors 68000

    TheReef

    Joined:
    Sep 30, 2007
    Location:
    NSW, Australia.
    #5
    Be very very careful, handling CRTs (especially old ones), is best left to the experts.

    I'm not sure if this is related to your problem exactly, but my Classic II experienced the checkerboard display issue, others have said washing the logic board helped (yes in water). (Certain capacitors were leaking and also needed to be replaced).
     
  6. harry2 thread starter macrumors newbie

    Joined:
    Oct 26, 2008
    #6
    mac plus half screen?

    Thanks for replies , I spent last night removing the boards, disconnected everything possible, cleaned and checked all visable joints, I found nothing
    obvious, except for the remains of the adhesive, (used to fix the instruction sheet to the side of the video board?)this did take some removing! but now the entire board was cleaned with contact cleaner, it looked fine, It did not take long to rebuild, and yes powered up fine with full screen! few small adjustments
    and all seems ok It would be nice to know exactly what caused this screen problem, but cleaning everything seems to have worked! one adjustment not
    explained is the voltage adjuster? there must be a test point to set this voltage
    correctly somewhere?..........harry
     
  7. DZ/015 macrumors 6502a

    DZ/015

    Joined:
    Mar 23, 2003
    Location:
    New England
    #7
    The voltage adjust pot is used to adjust the 5vdc power supply. You can measure this on pin 6 on the logic board connector. You should have 5.00 to 5.01 vdc at this pin. If not, adjust the pot.
     
  8. MacTech68, Nov 23, 2008
    Last edited by a moderator: Feb 8, 2011

    MacTech68 macrumors 68000

    MacTech68

    Joined:
    Mar 16, 2008
    Location:
    Australia, Perth
    #8
    Hi Harry,

    The old "Power/Sweep" boards in Mac 128K, 512K, 512Ke and Plus are all the same. They ended revising these at Revision D.

    The Yoke connector (large 4 pin connector towards the top of the board) often developed dry solder joints and needed resoldering or replacing. If it's gone a very dark brown color, then be careful as this means it's been running hot (arcing causes the heat), and the nylon plastic will be very brittle.

    The +5V adjust should be measured from the metal frame to pin 6 - it's the middle pin of the large connector on the motherboard (at the bottom of the case). Be very careful as the main switching transistor heatsink can be live and is adjacent to this!

    This might help:

    macintosh_plus_sm.pdf

    :)
     

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